1. Field of the Invention
This invention relates to the preparation of predominantly noncyclic poyalkylene polyamine products and more particularly pertains to a liquid phase catalytic process for synthesizing predominantly noncyclic poly(n-alkylene amines) with low heterocyclic amine content.
2. Prior Art
Heretofore, polyalkylene polyamine compounds and particularly polyethylene polyamine compounds such as diethylenetriamine, triethylenetetramine, and the higher homologs as well as the related carbon-substituted homologs have been conventionally produced by reacting an alkyl halide, e.g. ethylene dichloride, with an amine compound such as ammonia, ethylenediamine, and the like at elevated temperatures and pressures. Generally speaking, relatively high yields of predominantly noncyclic polyethylene polyamine compounds are obtained along with varying yields of heterocyclic amines, e.g. piperazine materials. These processes, while generally employed throughout the industry, suffer from serious disadvantages.
Exemplary shortcomings of these procedures include large amounts of energy required to produce reactants and expensive recovery procedures. The resultant hydrohalide salts of ammonia and the polyamines must undergo caustic neutralization to obtain the free polyamines. Separation of the desired free polyamines is difficult and disposal of the polluting by-products, such as the alkali metal halide salt, is expensive. Additionally, the products produced possess undesirable colorants, limiting use of the material in color-critical applications.
There are several procedures described in the literature for directly preparing predominantly non-cyclic polyethylene polyamines by the condensation reaction of an aminoalkanol compound and an alkylatable amine compound which do not require neutralization of the reaction product to obtain the desired salt-free polyamines.
For example, U.S. Pat. No. 3,714,259 to Lichtenwalter et al. describes a catalytic process for the preparation of lower polyethylene polyamines such as diethylenetriamine, whereby an ethyleneamine compound and an ethanolamine compound are contacted in the presence of hydrogen and a hydrogenation catalyst comprised of oxides of nickel, copper, chromium, and like metals, in liquid phase at a temperature of 140.degree. to 170.degree. C. This procedure produces only lower polyethylene polyamines. In addition, the reaction requires extended reaction times to provide acceptable conversions. Yet, when the process is carried out under conditions which provide an acceptable conversion rate, selectivity is sacrificed with attendant production of by-products such as piperazine and piperazine products. The resulting amine product also contains considerable hydroxyl content, another disadvantage.
We have now discovered an improved catalytic process whereby predominantly noncyclic polyalkylene polyamines and preferably poly(n-alkylene polyamines) may be produced from the condensation of an alkanolamine compound with an alkyleneamine compound under economically feasible short reaction times. The improved process provides conversion rates of reactants and selectivity comparable to or higher than those obtained by conventional processes which require neutralization with alkali, as described hereinbefore. Surprisingly, it has been discovered that the condensation reaction may be carried out under rather severe processing conditions, such as temperatures above about 250.degree. C. in liquid phase without the expected decomposition and excessive by-product formation. For example, it is known that polyalkylene polyamines, and particularly the higher homologs of the ethyleneamines such as triethylenetetraamine, tetraethylenepentamine, etc. are thermally degradable. Moreover, as more particularly explained in the examples contained herein, experiments have shown that total reactants conversion are drastically improved under these processing conditions while selectivity is substantially maintained as compared to the use of less severe processing conditions.
Although it has previously been disclosed that certain phosphoric acid compounds are effective as catalysts in promoting condensation reactions between several types of amines, and aminoalkanols generally, the reaction conditions are relatively mild and/or the condensation sites are limited. For example, U.S. Pat. No. 3,121,115 to Meuly teaches a process for amino-alkylating certain amines having a replaceable amino hydrogen, particularly aromatic primary and secondary amines, which includes heating the amine compound with an N-tertiary amino-alkanol at from 150.degree.to 250.degree. C. in liquid phase with continuous water removal in the presence of a phosphoric acid compound. The disclosed process requires long reaction times, a disadvantage mentioned hereinbefore, and the use of an N-tertiary aminoalkanol. Thus there is a limitation on the products formed and the possible sites for the condensation reaction to occur. In contrast, the alkyleneamine-alkanolamine reaction of the instant invention allows polycondensation, while being surprisingly selective to the predominantly noncyclic, linear product.